Not particularly severe for various reasons;
- I'm not sure if you ship with syslogging enabled by default
- Even if you did, it might not be exploitable
- And you don't listen on the snmp network port by default anyway.

Still,
If we look at
ucd-snmp-4.1.2/snmplib/snmp_logging.c: snmp_log_string():
...
#if HAVE_SYSLOG_H
  if (do_syslogging) {
    syslog(priority, string);
  }
#endif
...
That syslog() call is mising "%s" as a second argument. Classic format
string bug.
Probably best to patch for the next release, but I doubt it warrants an
update unless you _do_ enable syslogging by default.
Check it out and update this bug if syslogged is enabled by default.